5 volt power feasibility

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I'm looking in creating a project using the atmega32u2. This design will have multiple uses. But in all cases it will run off power from various gaming console controller ports.

 

source usb: I.e xbox. this will be usb voltage so in this case not really issues. The chip will run as a usb device within the operating voltage.

source +5: Most all consoles will supply 5 volts, and the current rating will go from 20ma to 400ma. As long as it can power the mcu (don't see why not) this will be ok.

source +3.3: This case I'd need to step up my voltage. This mode require specific timing with a 16mhz crystal and 3.3 is outside the acceptable clock range for the chip.

 

There is one more brick I need to throw in here.  This device will also have to power a atmega328. and a controller. The 4 devices will be linked together.

 

illustration.

[1 controller]->[2 device using atmega328]->[3 this device atmega32u2]-> [4 console]

 

So 1,2 and 3, all need to depend on power from 4. The total current is :

1 most controller range from 5 to 20 ma. I have see some a bit higher

2 atmega328 6.75mA @ 5 volts

3 guessing a bit more then the 328

4 20-400 ma depending and some combination will just not work.

 

 

This is the reason I said "feasibility" and I know a lot if detail is left out here as I don't have data for all possible scenarios. I'd like to achieve this without a battery or having to use an additional voltage source.  As it stands my main concern is the 3.3 or any other scenarios where the MCU may require more then the supplied current. One option is to use the pololu device, http://www.pololu.com/catalog/pr... but would that work out well enough? Most of what is going on here is logic level switching and the occasional controller motor turn (i.e rumble). Though the timing in the mega328 is very critical so I must maintain 5 volts at all times.

 

The easy solution here is stable power from an external source. I guess my question is, is this feasible without an external source, or is it way to hard to tell without experimentation? Only brainstorming ideas here, if there is no solution to this, ill opt for the external power source.

 

 

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You’ll probably find the m328 will work fine on 3V3 at 16MHz. Not guaranteed though.
Or just choose a more suitable part.
[edit] i see we’ve been down this path before.
You’ve got conflicting requirements to voltage, current and speed. Either form a compromise or look for another solution. Sounds like my day job.

Last Edited: Tue. Feb 13, 2018 - 10:20 PM
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Personally, I would use an Xmega32e5 instead, put an LDO in front of it and call it done. The architecture is similar enough so it's not too difficult to switch over.
This is only an option if you don't rely on the Arduino framework, of course. I you do, just take any of the Arduino compatible boards that already work with 3.3V.
If you do need a step-up, choose one that uses the SEPIC architecture, they are the most suitable for that application.

"Some people die at 25 and aren't buried until 75." -Benjamin Franklin

 

What is life's greatest illusion?"  "Innocence, my brother." -Skyrim

 

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According to the datasheet 328PB requires about 3.78 V to run at 16 MHz. Dependency is linear between 10 MHz @ 2.7 V and 20 MHz @ 4.5 V

Not sure that 6.75 mA is real maximal current for it. May be higher at startup.

 

[edit]: corrected required voltage for 16 MHz.

 


Qoitech AB, The Home of Otii Arc, an SMU for every developer

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Last Edited: Wed. Feb 14, 2018 - 09:57 AM
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Yabusame wrote:
According to the datasheet 328PB requires about 1.98 V to run at 16 MHz. Dependency is linear between 10 MHz @ 2.7 V and 20 MHz @ 4.5 V

 

I really don't know how you get 1.98 V. I saw the same page in the datasheet and I get 3.78 V for 16 MHz.

"Some people die at 25 and aren't buried until 75." -Benjamin Franklin

 

What is life's greatest illusion?"  "Innocence, my brother." -Skyrim

 

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"This forum helps those that help themselves."

"How have you proved that your chip is running at xxMHz?" - Me

"If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand." - Heater's ex-boss

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Whoops... You're right. It's 3.(7) V Missed a minus at 4.985 offset, my bad.

I'll correct my previous post as well.

 


Qoitech AB, The Home of Otii Arc, an SMU for every developer

Check out Otii solution at www.qoitech.com

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"Arduino framework" - No but I use v-usb frame work and that is a bit banging usb firmware. If that clock is not exact it falls apart. The device [2] is an existing product, part swapping it out. I certainly can try running this at 3.3 but I feel I will have issues. It it were one mcu I could predict and counter with crc but  having two mcu's on deck...

 

" choose one that uses the SEPIC architecture" Yeah pololu has that. https://www.pololu.com/product/2121 I can not tell if this chip has any ic's that require programming. Is this close/proprietary or could I use the parts on my design.

Last Edited: Wed. Feb 14, 2018 - 01:49 PM
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Let me get this straight, you have a mega32u2 (with hardware USB) and you are using v-usb to bit bang usb?

David (aka frog_jr)

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why don't you run at 12MHz, there you only need 3.06 V

 

Not sure that 6.75 mA is real maximal current for it. May be higher at startup.

I don't think at startup, but your IO's will probably use some power. 

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no, the 328 has the usb bit banging on it.  (device [1] illustrated uptop). Oh and the 328 code space is 29k already, so using the one 32u2 chip is out as I need at least 10 more k of code to add. I though about about another usb chip with more space and pins and this would give me the option of all the program on one chip but my existing users that have the 328 design will be forced to buy a new product. So there is that consideration as well. This new device is meant to be an add-on to an existing product.

 

why don't you run at 12MHz, there you only need 3.06 V

Sorry for any confusion. The 328 does run 12mhz but the added chip (32u2) that will be in the line of communication here, needs to be 16mhz to handle the data speed of the n64 console.  The protocol is coded in ASM and 12mhz is just not enough. Also I think the full speed usb requires 16 as well, not %100 on that.

Last Edited: Wed. Feb 14, 2018 - 04:31 PM
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what about a  charge pump, the LTC3200ES6-5 ?  Ideally I'd want a range up to 5 volts. Putting 5 volts in to this is out of range.

Last Edited: Thu. Feb 15, 2018 - 04:20 PM
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Well 5V is out of range but below Absolute Maximum. So it won't destroy the device but it may cause undesired behavior.

I expect the output voltage to rise well above 5V, which is something you don't want here. Even if it still works acceptably, it's a bad design choice.
The reason why I suggested to use a SEPIC converter is that these are meant to have an output voltage that's within the input voltage range. Or in other words, the input voltage can be lower, equal, or higher than the output voltage and the output still remains constant. So this is exactly what you're looking for.

 

Edit: You might actually find a charge pump that allows for the input to be higher than the output if you search for it long enough. Or you cold choose a two staged system with the charge pump raising the voltage to maybe 6 or 6.5 V and then lower it again with an LDO to 5 V.

"Some people die at 25 and aren't buried until 75." -Benjamin Franklin

 

What is life's greatest illusion?"  "Innocence, my brother." -Skyrim

 

Last Edited: Thu. Feb 15, 2018 - 04:29 PM
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You might actually find a charge pump that allows for the input to be higher than the output if you search for it long enough.

Maybe this is more suitable?

http://www.ti.com/product/TPS60150

 

"Maximum Output Current: 140 mA" -- is cutting it close as I designed for 200ma.

 

Last Edited: Thu. Feb 15, 2018 - 04:52 PM
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S_K_U_N_X wrote:
Maybe this is more suitable? http://www.ti.com/product/TPS60150

 

By looking at the efficiency diagrams, I suspect that this device actually does incorporate both a charge pump and an LDO. So if the output current is not sufficient, you can build that yourself. You can do that with an inductive step-up as well of course.

"Some people die at 25 and aren't buried until 75." -Benjamin Franklin

 

What is life's greatest illusion?"  "Innocence, my brother." -Skyrim

 

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, I suspect that this device actually does incorporate both a charge pump and an LDO.

 I would not be surprised.